The present invention relates to a method of and apparatus for selectively producing a temperature rise in a highly localized area of a medium. The medium may be heterogeneous, and the differential temperature rise may be controlled.
A phenomenon referred to as chemical relaxation was disclosed in 1954 by M. Eigen, Discussions of the Faraday Society, volume 17, pages 194-205. He described a method of producing a temperature rise using Joule's heating with a conducting electrolyte solution. In this method, typically, volumes of around 1 ml. of a homogeneous system are used, see also Czerlinski and Eigen, Z. Elektrochem, vol. 63, p. 652 (1959).
The method of the present invention is directed to producing differential hyperthermia to volumes much smaller than 1 ml. Further, the method is applicable to heterogeneous systems, such as cellular systems and tissues.
The method uses magnetizable particles which are very small in size, preferably in the order of 0.1-1.0 microns for biological applications, but generally in the range of 0.05-10 microns. Such magnetizable materials are intended to include both ferromagnetic and ferrimagnetic materials. Particles of the first size range are subcellular and can be selectively localized within the system to thereby achieve a highly localized hyperthermia. An external alternating magnetic field is applied to the particles. In the disclosed apparatus, the magnetic field is pulsed, and has a high magnetic field component but a relatively low electric field component.
With the particles in the preferred size range, coupling between the magnetic field and the surrounding matter becomes substantial. Further, by relating the frequency of the applied magnetic field to the particle size in a manner to be disclosed below, dissipative heat coupling from the small particles in the heterogeneous medium to the localized neighboring areas of the medium is maximized.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.